Heavy feed hydroconversion in ebullated bed mode has been used for over 50 years and it has undergone many evolutions that have formed the subject of many patents and publications.
In 1968, S. B. Alpert et al. described in document U.S. Pat. No. 3,412,010 a method wherein the feed is fed with hydrogen into the bottom of the reactor in a distribution box arranged below the catalytic bed, and mixed with part of the recycled liquid withdrawn downstream from the catalytic bed.
Recently, an article by Rana et al. (Fuel, 86, 1216-1231, 2007) described the method and the operating conditions characteristic of ebullated-bed reactors for residues hydroconversion.
A large number of patents describe that a hydrocarbon feed is introduced with hydrogen and the fluids flow in ascending mode through a catalyst bed under velocity conditions allowing fluidization of the catalyst and therefore expansion of the bed. The latter are also provided by recycling a liquid fraction circulating in a recycle line and a recycle pump allows the liquid to be reinjected into the reactor bottom. Further details are given, among other things, in documents U.S. Pat. Nos. 6,153,087, 6,436,279, 3,412,010, 4,792,391 and 4,990,241.
Among these documents, it can be noted that FIG. 1 of documents U.S. Pat. Nos. 4,792,391 and 4,990,241 perfectly describe the injection of the feed and of the hydrogen into the reactor bottom.
Besides, document GB-2,126,494 describes a particular device allowing injection of the gas and of the liquid into the reactor bottom.
Furthermore, patent U.S. Pat. No. 6,280,606 describes a method of converting a hydrocarbon fraction resulting from atmospheric distillation, followed by vacuum distillation of a petroleum crude. Distillation of the crude allows to separate a vacuum distillate (VD) and a vacuum residue (VR) that are then respectively subjected to hydrotreatment and hydroconversion in ebullated-bed reactors. The feed fed into the hydroconversion reactor is essentially liquid under the conditions of the process.
When the refiner wishes to upgrade a crude containing heavy fractions in large amounts, it may be advantageous to upgrade the heavy crude through moderate conversion and partial desulfurization so as to make the crude thus treated easier to integrate in conventional refining schemes. This operation is carried out in the vicinity of production sites through combination of atmospheric distillation, vacuum distillation and hydroconversion operations but this combination with a conventional refining complex is expensive. In some cases, it would therefore be advantageous to do without the distillation operation upstream from the hydroconversion process.
The applicant has found that it is possible to provide a new method allowing to carry out ebullated-bed hydroconversion of heavy feeds containing a significant proportion of vaporizable fractions under the hydroconversion conditions, without requiring initial upstream fractionation of the feed and without altering operation of the hydroconversion reactor.
The method according to the invention uses both injection of the feed to be treated into the top of the ebullated-bed hydroconversion reactor in the gas overhead and a device internal to the reactor for separation of the vaporizable fraction and of the liquid fraction.
The method according to the invention is advantageously applied for hydroconversion of petroleum feeds, notably for direct treatment, i.e. in the absence of a distillation stage upstream from said process, of crudes containing a significant fraction (above wt. 10%) of compounds whose boiling-point temperature is below 340° C.
The method according to the invention is particularly well suited for hydroconversion of crudes, preferably desalted, after flash under the temperature and pressure conditions at the crude production well outlet.